Motor driving control method and motor driving control apparatus

Abstract

A motor driving control method in which when the steering angular velocity is lower than a predetermined reference angular velocity, an actual motor drive current is inferred from a back electromotive voltage and an applying voltage in a three-phase brushless motor, and a limitation on the peak level of each of three-phase alternating current command waves is mitigated by permitting the interval between a pair of intersection points of a peak area of each of the three-phase alternating current command waves with a peak point neighborhood of a triangle wave to become approximately the same length as a dead time.

1. A motor driving control method for applying three-phase alternating currents as motor drive current from a three-phase bridge circuit to a three-phase brushless motor provided in a vehicle for steering assist, by performing PWM control in a triangle comparison method based on a command value determined in dependence on a steering angle, a vehicle speed, and other driving states and for performing current-feedback control with actual motor drive currents detected by shunt resistances, the motor driving control method comprising:
 judging whether or not a steering angular velocity is higher than a predetermined reference angular velocity; 
 when the steering angular velocity is lower than the predetermined reference angular velocity, detecting actual motor drive currents by the respective shunt resistances with the peak level of each of three-phase alternating current command waves being limited so that the interval between a pair of intersection points of a peak area of each of the three-phase alternating current command waves with a peak point neighborhood of a triangle wave, which waves are compared in the triangle comparison method, is made to be longer than the sum of a current detection time by the shunt resistances and a dead time for switching; and 
 when the steering angular velocity is higher than the reference angular velocity, inferring an actual motor drive current from a back electromotive voltage and an applying voltage in the three-phase brushless motor instead of detecting the actual motor drive currents by the respective shunt resistances, and mitigating the limitation on the peak level of each of the three-phase alternating current command waves by permitting the interval between the pair of intersection points to become approximately the same length as the dead time. 
 
     
     
       2. A motor driving control apparatus comprising:
 a three-phase bridge circuit connected to a three-phase brushless motor provided in a vehicle for steering assist; 
 a motor control circuit for making the three-phase bridge circuit output three-phase alternating currents as motor drive current, by performing PWM control in a triangle comparison method based on a command value determined in dependence on a steering angle, a vehicle speed, and other driving states; 
 shunt resistances for providing current-feedback of the motor drive current; and 
 steering state judgment means for judging whether the steering manipulation is at the time of an ordinary steering in which the steering angular velocity is lower than a predetermined reference steering angular velocity or at the time of a quick steering in which the steering angular velocity is higher than the reference steering angular velocity; and 
 wherein:
 at the time of the ordinary steering, the motor control circuit detects actual motor drive currents by the respective shunt resistances with the peak level of each of the three-phase alternating current command waves being limited so that the interval between a pair of intersection points of a peak area of each of the three-phase alternating current command waves with a peak point neighborhood of a triangle wave, which waves are compared in the triangle comparison method, becomes longer than the sum of a current detection time by the shunt resistances and a dead time for switching, and 
 at the time of the quick steering, the motor control circuit infers an actual motor drive current from a back electromotive voltage and an applying voltage in the three-phase brushless motor instead of the current detections by the shunt resistances and mitigates the limitation on the peak level of each of the three-phase alternating current command waves by permitting the interval between the pair of intersection points to become approximately the same length as the dead time. 
 
 
     
     
       3. The motor driving control apparatus as set forth in  claim 2 , further comprising:
 output voltage judgment means for judging whether or not the output voltage from a direct current power supply provided in the vehicle to the three-phase bridge circuit is higher than a predetermined reference output voltage; and 
 wherein the motor control circuit mitigates the limitation on the peak level of each of the three-phase alternating current waves under the condition that the output voltage of the direct current power supply is higher than the reference output voltage. 
 
     
     
       4. The motor driving control apparatus as set forth in  claim 3 , further comprising:
 engine rotational speed judgment means for judging whether or not the rotational speed of an engine provided in the vehicle is higher than a predetermined reference rotational speed; and 
 wherein the motor control circuit mitigates the limitation on the peak level of each of the three-phase alternating current wavers under the condition that the rotational speed of the engine is higher than the reference rotational speed. 
 
     
     
       5. The motor driving control apparatus as set forth in  claim 2 , further comprising:
 engine rotational speed judgment means for judging whether or not the rotational speed of an engine provided in the vehicle is higher than a predetermined reference rotational speed; and 
 wherein the motor control circuit mitigates the limitation on the peak level of each of the three-phase alternating current waves under the condition that the rotational speed of the engine is higher than the reference rotational speed. 
 
     
     
       6. A motor driving control apparatus comprising:
 a three-phase bridge circuit connected to a three-phase brushless motor provided in a vehicle for steering assist; 
 a motor control circuit for making the three-phase bridge circuit output three-phase alternating currents as motor drive current, by performing PWM control in a triangle comparison method based on a command value determined in dependence on a steering angle, a vehicle speed, and other driving states; 
 shunt resistances for providing current-feedback of the motor drive current; 
 steering state judgment means for judging whether the steering manipulation is at the time of an ordinary steering in which the steering angular velocity is lower than a predetermined reference steering angular velocity or at the time of a quick steering in which the steering angular velocity is higher than the reference steering angular velocity; 
 current detection means provided in the motor control circuit and configured to operate at the time of the ordinary steering for detecting actual motor drive currents by the respective shunt resistances with the peak level of each of the three-phase alternating current command waves being limited so that the interval between a pair of intersection points of a peak area of each of the three-phase alternating current command waves with a peak point neighborhood of a triangle wave, which waves are compared in the triangle comparison method, becomes longer than the sum of a current detection time by the shunt resistances and a dead time for switching; and 
 inference means provided in the motor control circuit and configured to operate at the time of the quick steering, for inferring an actual motor drive current from a back electromotive voltage and an applying voltage in the three-phase brushless motor instead of detecting the actual motor drive currents by the respective shunt resistances; and 
 limitation mitigation means provided in the motor control circuit and configured to operate at the time of the quick steering, for mitigating the limitation on the peak level of each of the three-phase alternating current command waves by permitting the interval between the pair of intersection points to become approximately the same length as the dead time.